Conventionally, organic compositions comprising a thermosetting resin such as a polyester, epoxy, and phenol, a reinforcing material such as glass fiber, a filler such as calcium carbonate, and an inorganic compound such as aluminium hydroxide which is dehydrated and decomposed by heat from an electric arc, and a switch using the organic composition have been disclosed, for example, in Japanese Patent Laid-Open No. 8-171847.
In such a switch, the blended inorganic compound such as aluminium hydroxide is subjected to dehydration reaction by the heat energy from the electric arc, and H.sub.2 O, O.sub.2 and O resulting from the decomposition react with and oxidize free carbon coming from an insulation substance of the organic composition, metal vapor or metal liquid droplets coming from a metal member. O.sub.2 and O change the free carbon to CO.sub.2 and CO, metal vapor to metal oxide having no conductivity, and reduce the amount of the carbon molecules, metal vapor and metal droplets, while H.sub.2 O cools the electric arc and quickly cuts it off, thereby reducing the amount of the conductive carbon or metal to be adhered inside of the switch box to avoid that the insulation property lowers after the cut-off.
However, the switch produced from organic compositions disclosed in Japanese Patent Laid-Open No. 8-171847, particularly that produced from a resin composition of fumaric acid neopentyl glycol propylene glycol type polyester actually showed only a small improvement in its insulating property after an electric arc was generated.
Having analyzed a substance adhered inside of such a conventional switch, the present inventors found out that a metal layer was formed, in addition to free carbon, from scattered molten metal droplets and a sublimated metal which were generated from the contact and the metal part of the component inside of the switch when the switch was turned on or turned off and the adhered metal layer had largely affected the reduction in the insulation resistance.
As a result of detailed analysis of this phenomenon, a surface layer having a small aluminium hydroxide content and a large resin content was found on the surface of the molded insulation member comprising the conventional organic compositions. The reason for this formation is as follows: when the above-mentioned conventional organic compositions are poured into molds for molding an insulation member, the compositions in the molds are plasticized, and the resin component in the composition is contacted with the metal surface to form a skin layer. The resin component in contact with the mold is gelled and cured in a relatively short time. Therefore, the skin layer formed from the resin component is thickened and the resin components fill the most part of the surface layer of the molded product. Accordingly, the aluminium hydroxide is contained in the surface layer of the molded product only in a small amount, the expected effect cannot be obtained.
This invention has been made for solving the above-mentioned problems and its object is to provide a polyester resin composition which allows the aluminium hydroxide to be present, in a sufficient amount, in the surface layer of the molded product, so that the aluminium hydroxide oxidizes the free carbon, sublimated metal and scattered molten metal liquid droplets generated by electric arc formed by cut-off of a large current, a switch using the polyester resin composition and a process for producing the switch.